Electron discharge apparatus



Dec, 29, P J. H. FREMLIN ELECTRON DISCHARGE APPARATUS Filed Dec. 11, 1940 /%46/V we 5:40 of //7 mental Patented Dec. 29, 1942 F F E Q .E

ELECTRON DISCHARGE APPARATUS John Heaver Fremlin, London, England, assignor to International Standard Electric Corporation,

New York, N. Y.

Application December 11, 1940, Serial No. 369,518 In Great Britain February 6, 1940 2 Claims.

This invention relates to electron discharge apparatus and comprises an improved method and improved means for setting up an electron beam. It is of particular advantage in electron discharge apparatus utilising the principle of electron velocity modulation referred to more fully in copending British application No. 32,815/39.

Numerous arrangements have been proposed for setting up electron beams particularly in cathode ray tubes. In apparatus using velocity modulation of the electron stream, the power handling capacity is dependent upon the intensity of the stream and the problem arises of setting up electron beams of intensity very large in comparison with that required in the ordinary cathode ray tube. Moreover, the means utilised must not interfere with the disposition of resonators along the electron beam.

According to the invention it is proposed to use a thermionic cathode of large surface area, that is, substantially greater than the required cross-sectional area of the electron beam, and to concentrate the emission from the large area into the necessary narrow beam by means of a magnetic field the lines of force of which converge in the direction of travel of the beam. Electrons leaving the cathode at each point have a velocity component in the direction of the line of force at that point, being under the influence of positive electrodes disposed along and at the end of the beam. They therefore follow closely the lines of force (actually taking helical paths about these lines) and are concentrated into a narrow beam of considerable intensity.

For the setting up of the requisite magnetic field a single multi-turn coil of axial length short compared with its mean diameter may be axially disposed with respect to the beam path.

According to another aspect of the invention an electron discharge device comprises means for producing a stream of electrons, means for modifying the velocity of the electrons in said stream, means for extracting energy from said modified electron stream and a magnetic circuit extending along said stream for producing substantially converging lines of magnetic force in the direction of travel of the electrons of said beam in order to concentrate the beam into a small cross-sectional area.

The accompanying drawing shows one method of carrying out the invention as applied to a so-called Klystron tube.

C is a large surface cathode for emitting electrons which are formed into a beam by any suitable accelerating means, for example, by an accelerating grid G and by the application of a positive potential to another portion of the tube structure, such as the resonators RI, R2, through which the beam is fired. The resonant chamber Bl serves in known manner to modify the velocity of the electrons in the beam. The electrons become bunched due to their changes in velocity. Resonant chamber R2 may then extract energy from the bunched electrons for application to any suitable work circuit. The electrons after passing resonator R2 are then collected by a collector or target electrode T. M is a multiturn coil of rather short axial length the lines of force L from which extend over the cathode C and target electrode T and converge in substantially straight lines along the desired path of the beam from the point where it enters the first resonator Rl to the point wher it leaves the second resonator R2, thus concentrating the electrons into a narrow beam of great intensity.

Divergency of the field and hence of the electrons at the end of the beam path remote from the cathode may be an advantage in permitting the use of a larger collector electrode surface of greater heat dissipation. In order to increase the rate of divergence of the magnetic lines of force extending from within the main focussing coil it may be desirable to provide a further axial magnetic field producing means such as the coil Ml behind the cathode, the coils Ml being fed with direct current in opposite directions so as to form a magnetic neutral point on the axis behind the cathode.

What is claimed is:

1. In an electron discharge device, a large surface cathode for producing a stream of electrons, a large surface collector electrode opposite said cathode, two resonant chambers spaced from one another between said cathode and collector electrodes and having a relatively small perforation in alignment with the centers of the cathode and the collector, one of said chambers serving to modify the velocity of the electrons in the beam passing therethrough, and the second to extract energy from the electrons becoming bunched between the two resonant chambers, and a multiturn coil of relatively short axial length around said resonant chambers and producing lines of force which extend substantially over the entire surfaces of the cathode and the collector electrodes and converge in substantially straight lines, having a small cross-sectional area along a path including the perforations of the two resonant chambers.

2. An electron discharge device according to claim 1 wherein a magnetic circuit is provided beyond the cathode to concentrate the electron beam in the direction of its travel, and a further magnetic circuit, the field of which is in the opposite direction to that of the first magnetic circuit, is provided behind the cathode in order to increase the divergence of the lines of force of the first magnetic circuit at the cathode and to provide a neutral point on the axis of the beam behind the cathode.

J OHN HEAVER FREIWLIN. 

